1. Field of the Invention
This invention relates to a double-sideband reduced (diminished) or suppressed carrier transmitters, incorporating the basic procedure of providing a separate nonlinear amplification means for the phase modulation component of a double-sideband reduced or suppressed carrier wave and a second path for the envelope modulation component to provide a high efficiency transmitter for said double-sideband waves.
2. Description of the Prior Art
Double-sideband waves are modulated waves having symmetrical upper and lower sidebands and may be generated in balanced modulators either operating at the final frequencies or at an intermediate frequency which is converted to a final frequency. The signal is generally amplified to a suitable power level in a conventional linear amplifier. Another method which may be used has been disclosed in prior U.S. Pat. Nos. 2,666,133 issued Jan. 12, 1954, 2,774,041 issued Dec. 11, 1956, 2,784,311 issued Mar. 5, 1957, 2,992,326 issued July 11, 1961, 3,012,209 issued Dec. 5, 1961, 3,120,642 issued Feb. 4, 1964 and 3,201,694 issued Aug. 17, 1965, and in the papers "Comparison of Linear Single-Sideband Transmitters with Envelope Elimination and Restoration Single-Sideband Transmitters" by L. R. Kahn, Proceedings of the I.R.E., Vol. 44, No. 12, December 1956 and "Single-Sideband Transmission by Envelope Elimination and Restoration" by L. R. Kahn, Proceedings of the I.R.E., Vol. 40, No. 7, July 1952. Additional information regarding the design of most of the circuit elements in this invention are provided in these patents and papers. The Envelope Elimination and Restoration (EER) method described in these patents and papers splits the SSB or double-sideband reduced or suppressed carrier wave into its two basic components, the envelope modulation component and the phase modulation component. The phase modulation component may be amplified in nonlinear high efficiency amplifiers and the envelope modulation component amplified in low frequency linear audio amplifiers. The envelope component is later reintroduced by use of an amplitude modulator. Recently, a system, similar to the envelope elimination and restoration system, has been used experimentally in transistorized equipment where linear amplification is inefficient and subject to substantial distortion. A paper describing this type of transistorized equipment is; "Design of a High-Efficiency V.H.F. Double-Sideband Diminished Carrier Transmitter Having Low Spurious Emission" by V. Petrovic and W. Gosling; Proc. IEE, (English) Vol. 121, No. 2, February 1974.
The fact that the phase modulation component in the EER system may be multiplied in frequency if the phase modulation is divided by the same factor of multiplication was disclosed in U.S. Pat. No. 2,666,133 issued Jan. 12, 1954. However, frequency division adds complexity and cost to the system and can introduce some distortion.
3. Summary of the Invention
The present invention substantially obviates one or more of the limitations and disadvantages of the described prior art arrangements.
This invention discloses means and methods for producing a double-sideband suppressed or reduced carrier signal having low spurious output and utilizing high efficiency circuits.
Another basic object, feature, and advantage of the invention, is that it allows the use of transistor amplifiers having substantial leakage between the input and output circuits of said amplifiers. The present invention allows the use of high efficiency nonlinear amplification and does not require the use of frequency division circuits and may be used at relatively high frequencies.
These, and other objects, features, characteristics, and advantages of the system and signal development techniques of the invention will be apparent from the following description of certain typical forms thereof, taken together, with the accompanying drawings.